Brouard Consulting

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Brouard Consulting

Paris, France

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Berest P.,Ecole Polytechnique - Palaiseau | Sicsic P.,Ecole Polytechnique - Palaiseau | Brouard B.,Brouard Consulting
50th US Rock Mechanics / Geomechanics Symposium 2016 | Year: 2016

Interest in Compressed Air Energy Storage (CAES) is rising. CAES facilities are designed to deliver full-power capacity in a very short time period, which implies high gas-production rates and multiple yearly pressure cycles. A decrease in gas temperature during a pressure drop depends upon gas pressure, withdrawal rate and cavern size. Thermal tensile stresses, resulting from gas cooling, may generate fractures at the wall and roof of a salt cavern. However, thermal stresses do not penetrate deep into the rock mass. These fractures are perpendicular to the cavern wall. The distance between two parallel fractures becomes larger when fractures penetrate deeper in the rock mass, as some fractures stop growing. These conclusions can be supported by field observations, closed-form solutions and numerical computations based on fracture mechanics. Copyright 2016 ARMA, American Rock Mechanics Association.


Berest P.,Ecole Polytechnique - Palaiseau | Beraud J.F.,Ecole Polytechnique - Palaiseau | Gharbi H.,Ecole Polytechnique - Palaiseau | Brouard B.,Brouard Consulting | DeVries K.,RESPEC
Rock Mechanics and Rock Engineering | Year: 2015

The applied deviatoric stress during most creep tests performed on salt samples is in the 3.5–20 MPa range. However, the stresses actually experienced in the vicinity of a salt cavern are much smaller. Any extrapolation is difficult to vindicate, as the dominant micro-mechanisms are strongly suspected to be very different in the low-stress and medium-stress domains. To answer this concern, a very slow creep test was performed on an Avery Island salt sample. To minimize the influence of even the smallest of temperature deviations during the test, the testing apparatus was placed in a remote gallery of the Varangéville salt mine, taking advantage of the very stable temperature conditions offered in an underground environment. The test was performed in multiple stages and lasted 42 months. The successive loads of 0.1, 0.2, 0.3, and 0.5 MPa were applied. Measured steady-state strain rates were of the order of 10−12 s−1, which are significantly faster than that extrapolated from creep tests performed at loads ranging between 3.5 and 20 MPa. © 2015, Springer-Verlag Wien.


Brouard B.,Brouard Consulting | Berest P.,Ecole Polytechnique - Palaiseau | Djizanne H.,Ecole Polytechnique - Palaiseau | Frangi A.,Polytechnic of Milan
Mechanical Behavior of Salt VII - Proceedings of the 7th Conference on the Mechanical Behavior of Salt | Year: 2012

Storage of natural gas in salt caverns had been developed mainly for seasonal storage, resulting in a small number of yearly pressure cycles and moderate gas-production rates. The needs of energy traders are changing toward more aggressive operational modes. Gas temperature changes and additional stresses generated by high-frequency cycling in a storage cavern are discussed. It is proved that when fast pressure changes or short-period gas pressure cycles are considered, the thickness of the thermally disturbed zone at the cavern wall is relatively small. Refined meshes of the disturbed zone are required when performing numerical computations.


Berest P.,Ecole Polytechnique - Palaiseau | Brouard B.,Brouard Consulting | Djakeun-Djizanne H.,Ecole Polytechnique - Palaiseau | Hevin G.,Storengy
Acta Geotechnica | Year: 2014

Rapid gas depressurization leads to gas cooling followed by slow gas warming when the cavern is kept idle. Gas temperature drop depends upon withdrawal rate and cavern size. Thermal tensile stresses, resulting from gas cooling, may generate fractures at the wall and roof of a salt cavern. However, in most cases, the depth of penetration of these fractures is small. These fractures are perpendicular to the cavern wall. The distance between two parallel fractures becomes larger when fractures penetrate deeper in the rock mass, as some fractures do not keep growing. These conclusions can be supported by numerical computations based on fracture mechanics. Salt slabs are created. However, these slabs remain strongly bounded to the rock mass and it is believed that in many cases their weight is not large enough to allow them to break off the cavern wall. Depth of penetration of the fractures must be computed to prove that they cannot be a concern from the point of view of cavern tightness. © 2013 Springer-Verlag Berlin Heidelberg.


Berest P.,Ecole Polytechnique - Palaiseau | Brouard B.,Brouard Consulting | Hevin G.,Storengy
EPJ Web of Conferences | Year: 2010

In 1997-1998, an abandonment test was performed in a 950-m deep, 8000-m3 salt cavern operated by GDF SUEZ at Etrez, France. In this relatively small brine-filled cavern, which had been kept idle for 15 years before the test, thermal equilibrium was reached. A special system was designed to monitor leaks, which proved to be exceedingly small. In these conditions, brine permeation and cavern creep closure are the only factors to play significant roles in pressure evolution. This test strongly suggested that obtaining an equilibrium pressure such that the effects of these two factors were exactly equal would be reached in the long term. Four years later, pressure monitoring in the closed cavern resumed. Pressure evolution during the 2002-2009 period confirmed that cavern brine pressure will remain constant and significantly smaller than geostatic pressure in the long term, precluding any risk of fracturing and brine seepage to the overburden layers. © 2010 Owned by the authors, published by EDP Sciences.


Berest P.,Ecole Polytechnique - Palaiseau | Brouard B.,Brouard Consulting
48th US Rock Mechanics / Geomechanics Symposium 2014 | Year: 2014

Four in-situ tests performed in salt caverns in France and Germany are described. The main objective of these tests was to increase our understanding of the long-term behavior of abandoned caverns. It is proven that, in the long term, when cavern brine has reached thermal equilibrium with the rock mass, pressure evolution is governed by cavern creep closure and brine micro- permeation through the cavern walls. An equilibrium pressure is reached when the closure rate exactly equals the permeation rate. In the shallow caverns described in this paper, equilibrium pressure is significantly lower than geostatic pressure, ruling out any risk of fracture onset at the cavern roof. Interpretation of these tests allows salt permeability to be back-calculated. Copyright © 2014 ARMA, American Rock Mechanics Association.


Berest P.,Ecole Polytechnique - Palaiseau | Brouard B.,Brouard Consulting
Mechanical Behavior of Salt VIII - Proceedings of the Conference on Mechanical Behavior of Salt, SALTMECH VIII | Year: 2015

In some laboratory tests, it was observed that after a rapid stress drop, the sign of the strain rate changed. A simple constitutive model is proposed that accounts for this phenomenon, which is called “rheological reverse creep”. Reverse creep also is observed following a rapid pressure increase in a salt cavern: in this environment, cavern volume increases over several days even when pressure is kept constant after the pressure increase. This phenomenon, however, results from different factors, among which rheological reverse creep is only one: numerical computations prove that the slow redistribution of stresses in the rock mass, or “geometrical reverse creep”, also plays a significant role. © 2015 Taylor & Francis Group, London.


Wang L.,Ecole Polytechnique - Palaiseau | Berest P.,Ecole Polytechnique - Palaiseau | Brouard B.,Brouard Consulting
Rock Mechanics and Rock Engineering | Year: 2015

Creep closure and structural stability of a cylindrical elongated cavern leached out from a salt formation are discussed. The Norton-Hoff creep law, or “power law”, is used to capture the main features of salt rheological behavior. Two failure criteria are considered: (1) shear stresses must not be larger than a certain fraction of the mean stress (dilation criterion); and (2) the effective stress at the cavern wall (actual stress plus cavern fluid pressure) must not be tensile. The case of a brine-filled cavern whose pressure is kept constant is discussed first. It is proved that creep closure reaches a steady state such that stresses in the rock mass remain constant. However, decades are needed to reach such a state. During the transient phase that results from the slow redistribution of stresses in the rock mass, deviatoric stresses decrease at the vicinity of the cavern wall, and onset of dilation is less and less likely. At this point, the case of a rapid brine pressure increase, typical of a tightness test, is considered. It is proved that during such a swift pressure increase, cavern behavior is almost perfectly elastic; there is no risk of dilation onset. However, even when cavern pressure remains significantly smaller than geostatic, the effective stress at cavern wall can become tensile. These results, obtained through numerical computations, are confirmed by closed-form solutions obtained in the case of an idealized perfectly cylindrical cavern; these solutions provide a better insight into the main structural features of the behavior of the cavern. © 2015, Springer-Verlag Wien.


Brouard B.,Brouard Consulting | Berest P.,Ecole Polytechnique - Palaiseau | De Greef V.,Ecole Polytechnique - Palaiseau | Beraud J.F.,Ecole Polytechnique - Palaiseau | And 2 more authors.
International Journal of Rock Mechanics and Mining Sciences | Year: 2013

Cavern creep closure rate was recorded in the SG13-SG14 salt cavern of the Gellenoncourt brine field operated by CSME at Gellenoncourt in Lorraine, France. Cavern compressibility and the evolution of cavern brine temperature first were measured. In this shallow cavern (250-m, or 800-ft, deep), which had been kept idle for 30 years, cavern-brine thermal expansion can be disregarded. To assess cavern closure rate, a 10-month brine-outflow test was performed, followed by a 6-month shut-in test. During the tests, brine outflow or pressure evolution is influenced by atmospheric pressure changes, ground temperature changes and Earth tides. From the average pressure-evolution rate, it can be inferred that the steady-state cavern closure rate is slower than 10-5/year or 3×10-13/s. © 2013.


Thoraval A.,INERIS | Lahaie F.,INERIS | Brouard B.,Brouard Consulting | Berest P.,Ecole Polytechnique - Palaiseau
International Journal of Rock Mechanics and Mining Sciences | Year: 2015

The most accepted strategy for abandoning solution-mined salt storage caverns involves filling the cavern with brine and sealing the well permanently. The sealing can be delayed waiting for the brine to reach thermal equilibrium with the surrounding salt. This concept is based on the principle that the cavern, once closed, will reach an equilibrium pressure that will assure the cavern's long-term mechanical stability.This article provides quantitative information about the evolution of abandoned salt caverns (the value of the equilibrium pressure, the time before thermal equilibrium is achieved, the rate of brine expulsion from the cavern, the time before the cavern closes up) from numerical simulations based on the state of the art related to the phenomena that affect the cavern after it is abandoned. The model reveals the conditions under which an excessive increase in the brine pressure in the cavern may appear, which can lead to the walls of the cavern being damaged. It also provides a basis for recommendations that could help to control these risks. © 2015 Elsevier Ltd.

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